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A century of biodiversity: some open questions and some answers

Roberto Cazzolla Gatti

To cite this article: Roberto Cazzolla Gatti (2017) A century of biodiversity: some open questions and some answers, Biodiversity, 18:4, 175-185, DOI: 10.1080/14888386.2017.1407257 To link to this article: https://doi.org/10.1080/14888386.2017.1407257

Published online: 08 Dec 2017.

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Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tbid20 Biodiversity, 2017 VOL. 18, NO. 4, 175–185 https://doi.org/10.1080/14888386.2017.1407257

A century of biodiversity: some open questions and some answers

Roberto Cazzolla Gatti

Biological Institute, Tomsk State University, Russia

ARTICLE HISTORY Received 2 March 2017; Accepted 16 November 2017

Introduction Some (partially or completely) resolved questions about biodiversity The study the biodiversity is not just an attempt to under- stand the differences ro similarities between , habi- (a) What is biodiversity? tats or genomes. It also includes an understanding of how Most ecological models that try to explain biodiversity are nature regulates the processes that characterise ecosystems too simplistic and are often considered outdated (Cazzolla and ensure their functionality. It means as well to increase Gatti 2011; Connell 1980). Moreover, recently, the prin- the ability to predict the impact of current and future ciples based on competitive exclusion (Gause 1934) for anthropogenic actions on nature (Midgley et al. 2002). the explanation of biodiversity have been criticised from Biodiversity is what makes the a unique planet. both theoretical and empirical approaches (Cazzolla Gatti In the Universe, for all we know, or at least in our galaxy, 2016a). life is the exception rather than the rule (Dick 1999). It has been, therefore, suggested that niches are impor- And even if a day when we are able to document the tant to attain a genetic equilibrium that favours species presence of living beings on other planets will come, (Levine and HilleRisLambers 2009) and facilitates the cre- this will also be an exception. The appearance of life is a ation of new niches (Gatti, Hordijk, and Kauffman 2017a). phenomenon that has always fascinated mankind since What has emerged is that to reach a thorough understand- without it, our human species would have never existed ing of the evolutionary dynamics of biodiversity, which and no hairless biped would have studied life, with great could somehow explain the current distribution patterns admiration, and destroyed it with equal force (Cardinale and mechanisms of coexistence, we must consider both et al. 2012). the biogeographic and phylogenetic approaches (Cazzolla Species themselves are a mystery like the very existence Gatti 2016b; Pimm et al. 2014). of life (Wiley 1978). Why has evolution led to the ‘endless beautiful forms’, as Charles Robert Darwin called them, (b) Why are there so many species in the world? instead of letting one, amazingly adapted, dominate the evolutionary line? The idea that life needs other life forms in order to con- In recent years the advancement of ecological sciences tinue to exist, and thrive, has been frequently stressed in allowed a better understanding of some fundamental bio- the last years (Bastolla et al. 2009; Cazzolla Gatti 2011). diversity patterns (Gaston 2000). In less than a few dec- Thanks to species by-products which emerged when the ades most of the answers to the key issues about biological first living organism appeared on Earth this has certainly diversity have been enriched with new hypotheses and favoured the evolution of other species (Wilkinson 2006). theories (Ricklefs 2004). However, many other questions Over time, biodiversity emerged (Cazzolla Gatti 2016a; are still open. 2017a; Guill and Drossel 2008).

CONTACT Roberto Cazzolla Gatti [email protected] This article was originally published with errors. This version has been corrected. Please see Corrigendum (https://doi.org/10.1080/14888386.2017.1416756). © 2017 Biodiversity Conservancy International 176 R. CAZZOLLA GATTI

A new formulation of the ecological niche concept – that the species themselves allow the enhancement of which no longer sees a niche as a static set of conditions niches in terms of space and number. Each species plays and rules referred to any species, but rather as a dynamic a fundamental role in facilitating the colonisation of the evolution of potential and unprestatable ‘biological spaces other species, by simply modifying the basic environ- dependent on the species diversity’ – has been proposed ment and exponentially increasing the available niches’ (Cazzolla Gatti 2011). This network of relationships is dimension (Cazzolla Gatti 2011). Niches emergence is enriched with new connections each time a node is pro- autocatalytically facilitated by the presence of biodiver- duced by the network (i.e. through facilitation, autopoiesis sity itself. The fact that biodiversity can be considered and autocatalysis; Gatti, Hordijk, and Kauffman 2017a). as a system of autocatalytic sets (Gatti, Hordijk, and Kauffman 2017a) offers a possible answer to the fun- damental question of why so many species can coexist (c) What are the main drivers of biodiversity in the same ecosystem. evolution? After a critical review of the different kinds of speci- (e) Can we explain biodiversity global gradients? ation, over the years many authors have attempted to understand why the competitive exclusion principle For over two centuries, scientists have tried to disentan- has long been considered as a general low to explain gle the spatial patterns of fine-scale and global biodiver- biodiversity (Connell 1980; Tilman 1994; Vandermeer sity gradients in order to understand how biodiversity is et al. 2002). Some of them argued that the likely reason distributed on the planet (Rahbek 1995; Wallace 1878). lies in the fact that ecologists have not questioned some Given that some places on Earth are home to more spe- of the principles of natural selection. A new conceptual cies than others, an important biogeographical property of model was recently proposed (Cazzolla Gatti 2016a). It biodiversity is the latitudinal gradient of species richness. was developed in an attempt to unify the new trends in Many hypotheses have been proposed – often empirically biodiversity and evolutionary science. It argues in favour tested – to become real theories (Hillebrand 2004; Kraft of the importance of avoidance of , coop- et al. 2011; Wilson and MacArthur 1967) in order to eration, biological history, symbiosis (endosymbiosis explain this distribution gradient. These have been divided and endogenosymbiosis) and three-dimensionality, as into two broad categories: biogeographical/evolutionary the main forces that structure the biological diversity and ecological hypotheses. Almost all of them are, how- of ecosystems. ever, not mutually exclusive and, at the same time, do not completely explain this gradient (Currie et al. 2004; Jansson and Davies 2008). (d) How is biodiversity arranged in space? However, one of the most corroborate ecological and Ecologists argued that the exceptional diversity of species evolutionary hypotheses (Hutchinson 1959; Pianka 1966) on Earth is, at least, partly due to the different ways in is that climate (C) influences net primary production which species that are potential competitors have evolved (NPP) in such a way that, by raising/lowering the availa- traits that make them specialised and able to partition the ble biomass (B), and so increasing/decreasing the number exploitation of resources (Chesson 2000; Finke and Snyder of individuals (I), it ‘controls’ the number of species (S). 2008; Loreau and Hector 2001; Schoener 1974). However, So far, the C→NPP→I→S causal relationship has not been it has been also suggested that biodiversity is autopoi- clearly demonstrated because it does not seem mediated etic (Cazzolla Gatti 2016a; Fath et al. 2007; Ulanowicz directly by biomass (Currie et al. 2004). In other words, 1998) and autocatalytic (Gatti, Hordijk, and Kauffman there is no reason to believe that areas with higher biomass 2017a), because it is a system able to produce more of its would also have higher biodiversity. It could also be that own complexity than that produced by its environment. a few species with many individuals accounts for most of Biodiversity (as an autopoietic and autocatalytic system) the biomass in the ecosystems. requests more energy (solar light) and dissipates more By suggesting that the latitudinal gradient of biodiver- entropy (waste disordered energy) than a not-autopoietic/ sity can be, instead, explained as differences in the fractal not-autocatalytic system. dimension of the ecosystem niches, it has been shown The biodiversity-related niches differentiation theory that it is not the number of individuals or the biomass (BNDT) has been proposed to stress that the process of that influence species richness, but rather the extent of niches differentiation is strictly addressed and driven climate and primary production on niche variables. In by species (Cazzolla Gatti 2011). This theory suggests other words, it has been proposed that biodiversity, in that the number of niches in an ecosystem depends on addition to being autopoietic and autocatalytic, is also the number of species present in a specific moment and fractal (Cazzolla Gatti 2016b). BIODIVERSITY 177

(f) How much does an area and volume influence have been resolved (Lenton 1998, 2004), whether Earth biodiversity? can be considered a unit of selection, and therefore Gaia can adapt according to Darwinian evolution, is still an The species–area relationship (SAR) is another old pattern open question. It has been recently proposed (Cazzolla studied in (Connor and McCoy 1979). Its implica- Gatti Forthcoming) why and suggested how, a Gaian tions are relevant for many ecological, evolutionary, con- system composed by biotic (the biosphere) and abiotic servation and biogeographic purposes. Conversely, the (the geosphere-atmosphere) interacting and coevolving associated Volume-Species Relationship (VSR) has been elements, should be considered alive, in any evolutionary almost ignored although it may play a fundamental role senses. It has been shown that without invoking teleology, in ecology (Cazzolla Gatti et al. 2017b), and it is relevant so without any foresight or planning, a Gaian planet can for many different ecological aspects, such as the estima- be considered a co-evolutionary system analogous to a tion of minimum viable populations and species ranges, multicellular body: a super-unit of selection. as well as the planning of protected areas, etc. This new Five situations according to which Gaia is able to repro- perspective was investigated, looking at the canopy height as a proxy of the ecosystem volume (a sort of ‘biospace’ duce and to transfer her planetary genome to other unin- according to Susmel 1980), which influences plant rich- habited or inhabited planets have been described. Then, ness in forest ecosystems (Cazzolla Gatti, Vaglio Laurin, it has also been suggested that Gaia can face exclusion– and Valentini 2017c; Cazzolla Gatti et al. 2017b). competition–coexistence states depending on the fitness of her biota compared to those of the other reproducing biospheres. This demonstrates that Gaia can reproduce (g) Is there a link between ecosystem functions and and evolve in competition- with other planets. biodiversity? Some deep implications arise from these pieces of evi- How biodiversity relates to ecosystem functions and dence (Cazzolla Gatti Forthcoming). productivity has been a widely studied and a highly con- Mechanisms such as trade-offs (Wilkinson 2006), troversial issue over the past few decades. Initially, many portfolio effect (Tilman et al. 1997), biodiversity-related research approaches (Grace 1999; Leibold 1999; Tilman, niches differentiation (Cazzolla Gatti 2011), facilitation Wedin, and Knops 1996; Tilman et al. 1997) showed that and avoidance of competition (Cazzolla Gatti 2016a) and the relationship between species richness and NPP could insurance hypothesis (Yachi and Loreau 1999) all contrib- be visualised as a hump-shaped or a modal curve, with ute to stabilise the effects of biodiversity on Gaia, making richness first rising and then declining with increasing this latter a liveable, and an alive, planet. productivity. However, subsequent theoretical and empir- ical research, including meta-analyses, seriously dimin- (i) What is the impact of economic growth on ished the acceptance of the modal pattern as a canonical biodiversity? relationship (Hooper et al. 2005; Thompson et al.2009 ). Field experiments to test the degree to which diversity Contrary to what many economists suggest (The Economist affects community productivity (e.g. biomass) have had 2013) development is not always good for Nature (Cazzolla variable results (Hector et al. 1999; Tilman, Wedin, and Gatti 2016c). In fact, the fact that biodiversity and eco- Knops 1996). However, a preliminary global analysis systems are fundamental to sustain humanity and life on shows a correlation between plant species richness and Earth is a well-accepted theory, but during the last three carbon in alive biomass with an hump-shaped distribution centuries (since the industrial revolution), heavy pressures (Cazzolla Gatti R. and Di Paola A., unpublished). due to overexploitation have been put on nature (Butchart et al. 2010; Daily and Ehrlich 1992). At the same time, environmental protection is gaining increasing interest (h) How Gaia’s biodiversity makes Earth alive? due to a better understanding of the interconnection The idea that life affects the development of the plane- between human wellness and ecosystem health (Ehrlich tary environment, which, in turn, affects the future evo- and Ehrlich 2012). lution of life in a co-evolutionary way is well-accepted One theory suggests the problem lies in that even if now (Gould 1988). Nevertheless, since the proposal of the will to follow a sustainable lifestyle in the ‘Western the Gaia hypothesis (Lovelock 1972) many criticisms have countries’ is increasing, many developing countries are been suggested (see Volk 2002 and Turney 2003 for a sum- currently experiencing their phase of economic growth, mary). Most of them are related to teleology, the absence threatening and overexploiting their environment. By of natural selection operated at universal scale and the lack comparing the trends of the living planet index (LPI) of planetary reproduction (Tyrrell 2013). Even if some of and the human development index (HDI) in an eco- the problems concerning the ‘internal’ logic of the idea nomic-ecologic historical analysis, it has been proposed 178 R. CAZZOLLA GATTI

(Cazzolla Gatti 2016c) that societies follow common Some open questions about biodiversity patterns of development, towards a ‘developed’ society In the previous section, a summarised review of the where each society exploits local, regional and sometimes answers (partial or almost final) to some of the big ques- global natural resources in order to reach its economic tions about biodiversity has been proposed. Here I will growth. resume some open questions that still remain unanswered. Further overexploitation of natural resources, during Most of these issues, still in need of a solution, will address the growing phase of human populations, would impede future research plans for biodiversity. to keep alive most of the global biodiversity and ensure the providing of ecosystem services that sustain humanity. (a) Why are some species abundant and others rare? (j) What are the effects of on biodiversity? Ecological communities are composed of species, some of which are very abundant, and others which are highly rare. Climate change alone is expected to threaten with It is commonplace to consider the high evenness and low extinction approximately one quarter or more of all dominance as an indicator of high diversity, but this is not species on land by the year 2050, surpassing even hab- always true for all ecosystems. It is interesting to observe itat loss as the biggest threat to life on land (https:// that usually a handful of species contributes to most of the chge.hsph.harvard.edu/climate-change-and-biodiver- abundance of a sample, while the rare species contribute sity-loss). One of the main reactions of ecosystems to to the diversity of the system. There is a great debate on climate variations is the change of species distribution. the role of rare and dominant species (Lyons et al. 2005; Displacements of entire biological communities to the Emery and Gross 2007). The first appears to ensure resil- poles and the mountain tops to cope with the rising ience (the ability to recover from a disturbance) of the temperatures and expand the distribution areas to past ecosystem, while the dominant species are often called prohibitive places have been revealed (Beckage et al. keystone species as they ensure the maintenance of eco- 2008; Thomas, Bulman, and Wilson2008 ). The same system functions (Gaston and Fuller 2008; Mouillot et al. species composition of ecosystems is changing (Bunker 2013; Smith and Knapp 2003). et al. 2005; Lemoine, Schaefer, and Böhning-Gaese Species-abundance distributions (SAD) and related 2007). The species richness changes and this affects plots have the ability to shed light on the processes that ecosystem function (Hellmann et al. 2008; Levinsky et determine the biological diversity of a given ecosystem al. 2007; Rahel and Olden 2008). Even the structure of (Cazzolla Gatti 2014; Magurran 2004). Nevertheless, there ecosystems is rapidly changing in response to climate is still a need for a much better understanding of the pro- variations (Banerjee, Cazzolla Gatti, and Mitra 2017; cesses that influence the relative abundance of species, Phillips et al. 2009; Biggs et al. x2007). and that determines why some species are abundant and There is much evidence suggesting how the grasslands others are rare (Magurran 2013; Messina et al. 2016). A and savannahs, along with coral reefs and mangroves, better understanding of the processes that shape diversity are among the most endangered ecosystems (Biggs et al. over both macroecological and local assemblage scales 2008; Del Grosso et al. 2008; Lough 2008; Salazar, Nobre, (McGill 2011) will be fundamental to answer the question and Oyama 2007). Within the American prairies trees around why species abundances are as uneven as they are. are expanding and replacing herbaceous plants, and fires no longer follow historical seasonal trends with the typ- (b) Is the intermediate disturbance hypothesis ical herbivores of these ecosystems moving northward testable? or, otherwise, to the tops of mountains. Individual spe- cies, by varying the distribution ranges, are also chang- It is well known in ecology that environmental distur- ing the dispersion centres and their abundances (Carroll bances may affect the diversity at a species community 2007; Moritz et al. 2008). Specialist species and those level (Gaedeke and Sommer 1986; Hubbell et al. 1999; with reduced areal receive special attention by ecologists Müller et al. 2002). However, the diversity can also mod- because they risk more than generalist species (Clavel, erate the severity of the disturbance leading to the varia- Julliard, and Devictor 2011; Doody et al. 2006). tion of the frequency, intensity or duration of the effective Yet, it has been shown (Hannah 2014) that climate biomass loss in community with different initial numbers change is also accelerated by positive feedbacks due to of species (Sousa 1984). Many studies have attempted to some species expansion (e.g. the albedo effect due to the empirically test the intermediate disturbance hypothesis invasion of glaciated areas by vegetation). (IDH). The IDH, originally presented as an explanation BIODIVERSITY 179 for plants and sessile species (e.g. corals and trees) diver- natural populations, which are reproductively isolated sity, argues that an intermediate disturbance frequency from other such groups’. However, he terms ‘reproduc- or intensity can maximise diversity (Hutchinson 1953; tively isolated’ should be taken quite loosely, allowing for Molino and Sabatier 2001). limited gene exchange (Coyne and Orr 2004). Nevertheless, the diversity-disturbance curve may The problem of BSC arises when working with asex- have a variety of different shapes and many communi- ual microorganisms, particularly bacteria. In this case, a ties show no IDH effect due to competition from either useful approach is to take into account that despite the exclusion or dominance, because many species are able relative free incorporation of novel genes in this group to use the third-dimensional space (i.e. volume) avoiding of species, there are some ‘non-exchangeable’ genetic competition in the two-dimensional one (i.e. the surface) sequences between lineages, because the recombinant (Cazzolla Gatti 2011). Similarly, especially at low-fre- form would kill or be harmful (Sherratt and Wilkinson quency disturbance, the IDH often does not apply to 2009). This fact can be a good way to discern if a bacterial mobile species because of reduced competitive exclusion species has ‘reproductively isolated sequences’ in order to (Stachowicz 2001) and to communities characterised by apply the BSC. high complexity of habitats and, therefore, with a greater Yet, given the gap between DNA-based concepts volume of niche (Cazzolla Gatti et al. 2017b). In general, (mainly for asexual species) and the traditional mor- the disturbance decreases species diversity only when it is phospecies notion (mainly for sexual species), the high in frequency or intensity in the experimental manip- question is how much genetic difference justifies a new ulations (Kondoh 2001). species? To better answer the question whether the IDH is cor- rect, it is important to consider that a disturbance for one (e) Are neutral approaches useful for species can be a benefit for another and that it is impos- understanding biodiversity? sible to know what a disturbance is without prior experi- mentation (Bertrand et al. 2009). Moreover, richness and Neutral models are based on the idea that a minimal set of evenness respond differently to disturbances and this can assumptions and variables could explain a system (Gotelli be the reason why IDH applies at some times and not oth- and McGill 2006). In ecology, random distributions are ers (Sommer 1995). To test the IDH, it is fundamental to assumed to be tested against different hypotheses. In other know life histories and dominance/rarity patterns of the words, the simplest explanation is frequently the best. The analysed community. theory of island biogeography (MacArthur and Wilson 2015) was one of the first null models in ecology. Then, Stephen P. Hubbell (2001) proposed the unified neutral (c) Is there a maximum amount of the global theory of biodiversity and biogeography (UNTB), which biodiversity? assumes that all species belonging to the same trophic If biodiversity is indeed autocatalytic (Gatti, Hordijk, level of an ecological community are ‘neutral’ in relation and Kauffman 2017a), does it follow a sigmoidal growth to their evolutionary fitness. This implies that there are over time, as every autocatalytic reaction normally does? no real differences between the niches of each species Consider, for example, the trends of the number of genera and their success being dictated by the randomness of during the Phanerozoic Eon (Rohde and Muller 2005), the moment. which follows a hyperbolic growth curve. If the answer Although this theory predicts very well the distribution to the above question is positive, this curve should (in of species by means of a dynamic balance of immigration, absence of major catastrophic events) eventually reach a speciation and extinction, its main merit is its ability in saturation and show a sigmoidal curve. Can we predict reassessing the importance of niches in the maintenance it by, for instance, the differential equation of the BNDT of biodiversity (Dornelas, Connolly, and Hughes 2006). (Cazzolla Gatti 2011)? In fact, the UNTB cannot be easily transferred in nature where a number of variables, such as environmental het- erogeneity, biotic communities, and coevolution, move (d) What is a species? the debate in favour of the differentiation of niches (that ‘The species – wrote Albert Mousson (1849), a Swiss phys- is: species are unique). icist and biology enthusiast – is the total of individuals, The lognormal distribution model fits more data sets of interconnected by descent and reproduction, maintaining biological diversity than the neutral model of biodiversity unlimited reproductive capabilities’. Later Mayr (1942) (McGill 2003). Yet, it has been shown (Gaston and Chown proposed the biological species concept (BSC) that ‘spe- 2005) that neutrality can be considered as the basis for the cies are groups of actually or potentially interbreeding subsequent separation of ecological niches. 180 R. CAZZOLLA GATTI

Thus, the open question is: what degree of prediction is (h) Is it possible to predict the effect of biodiversity possible with the neutral theory of biodiversity? on ecosystem functions? Ecosystem function is the basal processes of an ecosystem (f) Is the natural history of biodiversity a and includes, for instance, primary production, respira- (predictive) science? tion, nutrient cycling and detritivory. Numerous studies on terrestrial (Bertness and Leonard 1997; Tilman, Reich, Most of the hypothesis proposed for the coexistence of and Knops 2006; ) and aquatic (Covich, Palmer, and Crowl species does not take into consideration the importance of 1999; Power 1990; Swan and Palmer 2006) ecosystems contingencies and natural histories over biological diver- have shown a positive correlation between biodiversity sity. It has been suggested (Cazzolla Gatti 2016a) that a and ecosystem functions, such as productivity and respira- thorough understanding of the evolutionary dynamics of tion. However, it is still difficult to define one overarching biodiversity, which could somehow explain the current relationship between these two variables. It seems that distribution patterns and mechanisms of coexistence must there is a saturation of the ecosystem function (respira- consider the biogeographic and phylogenetic pathways tion, productivity, etc.) over a certain level of richness, (Cowie and Holland 2006; Faith 2002). However, natural which follows a sort of logistic curve (Schwartz et al. 2000; history has a negative reputation among classic ecologists Srivastava and Vellend 2005). Functional redundancy and because it is a descriptive and not experimental (which the specific species involved (and their abundances) are do not allow predictions) branch of science (as well as key elements in this relationship. astronomy and geology). Nonetheless, natural history is An emerging issue is that facilitation plays an impor- the study of the specific contingencies of places and a basic tant role in increasing community diversity, which in turn knowledge of it can strengthen the ability to predict bio- influences the ecosystem function (Bruno, Stachowicz, diversity patterns. Yet, other open questions follow: how and Bertness 2003; Cardinale, Palmer, and Collins 2002; the knowledge of the natural history of biodiversity can Cazzolla Gatti 2011). allow us to predict future changes in species composition? The predictability of this relationship still remains an What ecological prediction, based on the natural history open, and very relevant (also considering the current high of biodiversity, we could be able to provide? anthropogenic impact on ecosystems) question about biodiversity. (g) Are there predictable rules to evaluate the success of an invasive species? (i) How many species are too few to keep Alien species are rarely able to settle into intact ecosys- ecosystems healthy? tems, which have not been subjected to anthropogenic stresses such as pollution, fragmentation, selective logging The health level of an ecosystem is strongly dependent on or hunting, etc. (MacDougall and Turkington 2005; Vaglio its functionality (Schaeffer, Herricks, and Kerster 1988). Laurin et al. 2016). When an allochthonous invasion takes Given there is a relationship between biodiversity and eco- place, it is very unlikely for the invasive species to com- system functions, even if it is still not completely clear pletely eliminate the endemic one, which usually tends to and difficult to predict, the minimum number of species reduce its own density or migrate to neighbouring areas, needed to keep an ecosystem in a good status depends if it has the phenotypic plasticity to do so (DeWitt and on the above-mentioned considerations. If enlarged on Scheiner 2004). This could also be due to the fact that a global scale, this could provide an answer to the next diversity increases the stability of an ecosystem (Tilman, query. Reich, and Knops 2006). Though, in rare cases, resource and habitat limitations may lead to the extinction of native (j) How many groups of species (guilds) are needed species (Sax and Gaines 2008). to avoid Gaia collapse? Habitat similarity, invasion frequency, human distur- bances, evolutionary strategies (K or r selection) and spe- The fact that the biota on Earth can maintain in different cies richness of the invaded area contribute to predicting ways, even if not always clear, favourable conditions for the success of an invasive species (Kolar and Lodge 2001; living beings, is now accepted with a few minor oppo- Sakai et al. 2001). If we were able to measure all these sitions (Lovelock 2000; Margulis and Sagan 2000). The variables and to estimate the biodiversity of a site, could Gaia theory suggests that organisms interact with their we say with a high confidence whether an alien species inorganic environment on Earth to form a mutualistic– will survive (and supplant others)? synergistic self-regulating and complex system that helps BIODIVERSITY 181 to maintain and perpetuate the conditions for life on the Conclusions planet (Lenton 1988; Lenton and Lovelock 2000). This idea It has only been in recent years that we have witnessed proved that the biosphere and the evolution of life forms an alarming rate of extinction of species and the loss of affect ocean salinity, the stability of global temperature, the ecosystems which has attracted international attention. maintenance of a hydrosphere of liquid water, oxygen in 2010 was proclaimed by the UN the ‘International Year of the atmosphere, and other ecological variables that affect Biodiversity’ and was an attempt to capture the attention the habitability of Earth (Lovelock 2003). Trade-offs, by and imagination of the world to recognise and come to preventing that one or two species monopolise the planet, terms with ‘the issue of the inexorable depletion of the allow speciation (Wilkinson 2003). In fact, if one species planet’s environment as a result of the destruction of hab- would be good at everything, as a super generalist then the itats and ecosystems’. niche concept would be useless (Wilkinson 2006). From the discovery of agriculture, through the indus- We know that the huge biodiversity resulting from trial revolution and up to now, humans have reshaped trade-offs has a positive effect on Gaia because it stabilises landscapes, modified ecosystems and caused the extinc- the planet conditions more than if Earth were inhabited by tion of many species. just a few of species (Lenton and Wilkinson 2003). What The importance of biodiversity has been internation- we do not yet know, is how much biodiversity is needed ally recognised by the Convention on Biological Diversity to keep the planet alive. That is, how many species (or (CBD) of 1992. It identified three main goals for human- how many guilds) are necessary to the maintenance of ity: ‘(i) conserve biological diversity; (ii) use it sustainably; favourable conditions for life on Earth? In other words, and (iii) share the benefits derived from it in a fair and is there a kind of no-return point? Can we identify this balanced way’. number and the ‘fundamental’ species/guilds? The CBD asserts that signatory countries must meet ‘a significant reduction in the rate of impoverishment of bio- (k) How many, and which, species will adapt to diversity at the global, regional and national levels with a sudden anthropogenic climate change? view to contributing to poverty alleviation and to the ben- efit of all life on Earth’. A target was even added in 2007, Climate change is also affecting species and ecosystems, during the World Summit for Durable Development of the and is causing a loss of genetic diversity of populations (held in Rio de Janeiro), to the Millennium that are confined in a shrinking area (Campbell et al. 2009; Development Goals (MDGs). Hannah 2014). All this, however, has in no way stopped the loss of bio- Recently more attention has been put on the fact that the diversity on Earth. Economic and short-term interests of species themselves can increase (with positive feedbacks) most heads of states and multinationals, the indifference the consequences of climate change (Araujo et al. 2005). of many citizens and a growing world population, espe- All this demonstrates that climate, atmosphere and cially in developing countries, are likely to undermine any biodiversity are deeply integrated and that any alteration international agreement. If we do not stop immediately of the balance can have unpredictable effects (Williams the depletion of marine and terrestrial habitats, the study et al. 2008). The problem lies not so much in the change of biodiversity will be considered as the shortest duration itself, given that the Earth over a 4.6 billion year period has science that has ever existed. undergone enormous climatic and geological upheavals At this point, it is critical for us human beings to under- (Crowley 2000), but rather in the rapidity of the change. stand that equality holds in the needs, feelings, rights, The Gordian knot is the velocity with which these cli- duties, sense of belonging to the Earth, in accordance with matic changes are happening (Loarie et al. 2009). Up to the universal laws of Nature, but that diversity is, instead, now species have had (evolutionary) time to adapt to the in the complexity and wonder of that universal exception slow physicochemical changes that occurred on the planet that is Life. Trying to answer some of the questions related (and they, in turn, moderate them with feedbacks). Today, to biodiversity is an attempt to know it better, to protect however, we are seeing rapid and radical changes that have it more. occurred in just a few decades, mainly since the start of the industrial revolution (Burrows et al. 2011). ORCID I would argue that the answer to how species will adapt to this sudden change of their ecosystems, is one of the Roberto Cazzolla Gatti http://orcid.org/0000-0001-5130- most important questions of the Millennium. 8492 182 R. CAZZOLLA GATTI

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